The present invention is directed to creating in-mold and in-line decorated articles having higher quality than previously attainable, greater permanence than previously available, using molding techniques previously excluded, using processes and materials previously excluded, and offering improvements in yield, throughput and scrap rates. The present invention provides images of near photographic quality that are highly resistant to fading, chemicals and abrasion that can be produced using both thermoplastic and thermosetting processes. The present invention makes possible new in mold and in-line capabilities and provides new or improved opportunities for product decoration and for product labeling where permanence, long life, safety labeling, product identification, ownership or serialization labels, or production lot identification is needed.
Product manufacturers place a high value on the ability to deliver a product with a high quality graphic surface. This has traditionally required a trade-off between the quality of the image and the permanence of the image and its print media. The highest quality achievable has been to lithographically print adhesive labels, which are applied after aforesaid articles have been molded. These suffer from poor adhesion to many types of materials resulting in decorative labels that peel and degrade the appearance of the product. Loss of adhesion is exacerbated by environmental factors such as moisture and large changes in temperature and is particularly acute in outdoor applications. The loss of labels containing safety related information is obviously a much more serious issue. Labels on products used by small children also present a choke hazard should the labels come off. In many cases information is placed onto the article using other post-molding decorating techniques such as heat transfer and pad and screen printing. These techniques result in the lowest quality image and are generally limited to one or two colors in relatively non-complex designs. In many cases, an image such as a logo or lettering is actually a part of the mold creating a raised area that receives the transferred color. Both of these techniques also add complexity to the manufacturing process by adding a post-molding step wherein the article is given its graphic image. Not only do these techniques add cost and manufacturing cycle time, but aforesaid techniques also introduce opportunities to convert a part into a quality reject if the image application is not done perfectly. Neither adhesive labels nor post mold decorating techniques involving transfer of image or color can effectively decorate over compound curvature areas or the sides of raised areas. Current art is essentially limited to flat or single curvature surfaces.
The shortfalls inherent in aforesaid post molding decorating techniques have resulted in the development of in-mold decorating techniques. In-mold decorating is characterized by the preparation of graphics, normally using screen-printing techniques on a polymer film material of composition compatible with the polymer to be used in molding the part. The film traditionally used for said in mold decorating is clear allowing the underlying molded polymer to show through. Many techniques use complex multi-layered films in an attempt to achieve a satisfactory in-moldable product. The printed film is normally placed into the mold so that the molten polymer flows over the ink, which is trapped between said film and said polymer. Temperatures and pressures characteristic of said technique drives requirements for screen printing inks that can withstand said process. The graphic detail quality achievable by said techniques is limited by the environment in which said inks must remain stable and not wash out or flow with the molten polymer. The cost of screen printing, with the requirement to separately deposit each color, results in total costs that diminish the competitiveness of in-mold decorated products made using said technique.
There is a plurality of reasons why yields of good parts are lower than desired by manufacturers when using said in-mold decorating. Causative factors include damage to the graphic image on the surface of the sheet during placement or molding, damage to the sheet itself during molding and lack of stability of the printed sheet in the mold during molding. Said graphic image damage results primarily from the robustness of the inks and lack of protection of same from the temperatures and pressures common in said molding processes. Said sheet damage results primarily from stretching or penetration of said sheet during molding due to the pressures of molding and the flow of molten materials over the sheets to their edges. Said lack of stability involves the movement of said printed sheet within the mold due primarily to the flow of molten material over said sheet causing said sheet to slide with respect to the mold surface or to lift from said mold surface. Said sliding results from insufficient coefficient of friction between said sheet and said mold surface. Said lifting results from said sheet presenting too much cross section to the flowing molten material, particularly when the entry of said molten material is not within the boundaries of said graphic sheet and said molten material must impinge upon the vertical edge of said printed sheet. Said lifting problem is exacerbated by thicker printed sheets, which may be used to provide the needed tensile properties. Common techniques used to enhance said stability include inducing electrostatic charges between said sheet and said mold surface to prevent movement during molding, texturing said mold surface to increase friction between said sheet and said mold surface, and use of detents or pockets in the mold to constrain said printed sheet. Problems inherent in using said electrostatic charge techniques include the inability to maintain said charge at a high enough level and for a long enough period to properly complete the molding process. The dissipation of said charge is accelerated by the typical marginal dielectric characteristics of said printed sheet. Said surface texturing and use of detents or pockets are currently the best available options either used in lieu of or in concert with said electrostatic charging.
Some of the shortcomings of both post molding decorating and traditional in-mold decorating have been partially overcome in the area of thermoplastic compression molded products where a printed sheet has molten polymeric material fused to its non graphic surface. Compression molding using a billet approach falls into the category of a low stress technique thereby overcoming the problems inherent in highly tortuous techniques such as injection molding. U.S. Pat. No. 4,861,644 disclosed the printing using various techniques, including offset lithography, of microporous substrates. U.S. Pat. No. 4,892,779 discloses the fusion of a printed microporous sheet to other materials using a variety of molding techniques. Disclosed, but not claimed is injection and blow molding of polyolefins. U.S. Pat. Nos. 5,591,384, 5,626,339, 5,637,329, and 5,800,757 all disclose the manufacture of thermoplastic products with graphics molded into the surface of the product during manufacture using low stress molding techniques such as compression and structural foam molding. These patents cite the use of polymers which are compatible with the polymer used to make the sheet which is in-molded to said polymer. While U.S. Pat. No. 5,512,227 discloses use of polyolefin films and U.S. Pat. Nos. 4,418,033, 4,650,533, 5,227,222, 5,338,396, 5,514,427, 5,536,539, 5,698,283, 5,705,255, 5,707,472, and 5,795,527 disclose use of non-polyolefin films in injection molding applications, they demand a multi-layer xe2x80x9csandwich,xe2x80x9d some involving adhesives to be an effective method of in-molding graphics during injection molding. Several of these techniques also require post-molding stripping of carrier sheets or layers from the finished part. Other patents, such as U.S. Pat. No. 5,676,981, require specialized techniques such as heating the graphic sheet to assure good adhesion and stability during the injection molding process. Other techniques such as described in U.S. Pat. No. 4,418,033 and U.S. Pat. No. 4,369,157 require a continuous strip of in mold decorating material to be repeatedly advanced between each mold closure; this routinely introduces errors in alignment of the image to the part resulting in a quality reject. Still other techniques such as disclosed in U.S. Pat. No. 4,330,578 and U.S. Pat. No. 5,629,029 require specialized molds or double injection steps to accomplish the in-mold decorating operation. Still other techniques for blow molding such as disclosed in U.S. Pat. No. 4,808,366 and U.S. Pat. No. 4,983,348 do not result in actual permanent fusion attachment of the graphic image sheet to the finished part. Still other techniques such as disclosed in U.S. Pat. No. 4,427,615 require pins in the mold upon which to hang the printed sheet to be inmolded.
In summary, existing methods of achieving said in-molded graphics generally depend on the similarity of materials between the graphically printed film and the substrate material to which the graphic is molded. Said methods address only thermoplastic applications. Where the use of dissimilar materials is disclosed there are complex techniques, such as multi-layering, required to affect the molding. The current state of the art offers no techniques for in-mold decorating with lithographically printed images using high stress manufacturing techniques such as injection molding. Since the majority of current molding is injection, there is a need for a method of economically achieving high yield, high throughput in-mold decorating manufacture of high quality graphic products. The current state of the art offers no techniques for introduction of a three dimensional graphic into the cavity of a mold to produce a dimensional part decorated in the mold with graphics on all top and side surfaces. Since most polymeric materials undergo shrinkage during post-molding cooling, there are issues with in-mold decorating techniques not matching the shrink rate; the current state of the art does not offer techniques for in-mold decorating where the image will automatically exhibit the same shrink rate as the polymer into which it is molded.
In order to overcome the deficiencies in prior art it is necessary that a method be developed to provide a system solution. The system solution of the present invention provides a printable sheet of not greater than ten mil thickness that can survive the tortuous injection molding environment and which is in-moldable with a wide variety of thermoplastic and thermoset materials; a family of inks that produce the highest quality images and can survive the molding process while also exhibiting excellent flexibility and resistance to fading in UV light; a family of coatings that aid the molding process and provide added permanence to the printed image in abrasive, chemical, or UV light exposure environments; a printed and coated sheet that can, if needed, be thermoformed to fit a complex mold face geometry; techniques for efficiently and positively placing and holding the printed sheet in the mold; high stability of the printed sheet in the mold during molding; and which is effective in a wide variety of molding techniques.
The system of the present invention exhibits the ability to place the aforesaid mentioned single layer printed and coated sheet into molds heretofore used for undecorated product manufacture and to produce an in-mold decorated product.
With respect to said printable sheet, there is a plurality of precipitated silica filled micro-porous sheet materials commercially available in the marketplace. Such materials exhibit varying degrees of robustness in the tortuous injection-molding environment. Material sold by PPG Industries, Pittsburgh, Pa. under the trade name MiST(trademark) is, when properly coated as explained herein, found to be satisfactory for the most demanding molding environments including thermoset applications where the material will be exposed to high temperatures for extended time periods for curing. Other materials, such as Daramic(trademark) manufactured by Daramic, Inc. of Owensboro, Ky. are generally satisfactory for thermoplastic injection molding applications if treated using coatings to improve their tensile properties and stability in the mold. Use of surface treatment coatings make ten mil thickness material suitable in all applications and makes seven thickness material suitable in many applications.
With respect to said inks, there are families of satisfactory lithographic, gravure, flexographic, and screen inks available in the marketplace from a number of sources by referring to inks suitable for use with PPG Industries Teslin(copyright) printable sheet. The use of such inks is an essential element in obtaining a quality print on silica-filled microporous sheet materials. Reference is made to the Grafusion(trademark) series of lithographic inks and the GRA series of screen inks which have been optimized for the aforementioned silica filled micro-porous materials and which demonstrate the flexibility and robustness to provide and maintain a high quality image through a tortuous injection molding process. Both of these series of inks exhibit exceptional fade resistance in prolonged UV exposure. These inks are available from Pinnacle Products Group, Ltd. of Dayton, Ohio. Such inks comprise a pigment and carrier which are formulated to withstand temperatures of up to 600xc2x0 F.
With respect to said coatings, there are families of UV energy cross-linkable coatings that provide the said printed silica-filled microporous materials with the performance enhancements essential for successful high yield molding of articles. By the nature of their molecular level changes during curing such coatings enhance the tensile properties of the printed sheets reducing the tendency of the sheet to stretch as molten material flows over the sheet to its edges. Increasing the tensile properties also allows the use of thinner material such as seven mil thickness; this is important because it reduces the cross section presented at the sheet edge where an excessive thickness induces disruption of the material flow causing said sheet to lift from the mold surface. The increases in tensile properties are also of value in minimizing stretch thus making the printed sheets usable in a continuous roll fed sheet extrusion process where graphics are fused to extrudate as it is produced. By the nature of the molecular changes that occur during curing the coatings also protect the ink during the molding process and provide said printed sheets with an increased surface coefficient of friction which significantly enhances the stability of the printed sheet within the mold during tortuous molding processes. Such sheet stability lowers the potential movement or float of the printed sheet as molten material flows over the sheet to its edges; the stability is essential to achieving high yield during tortuous molding processes. The increased coefficient of friction is also an essential performance factor if the printed articles are to be used in underfoot applications where slip resistance is an important safety issue. When needed such coatings can be formulated, and are commercially available which also enhance the resistance of the printed sheets from degradation by chemicals such as petroleum distillates and solvents which could contact the surface of the product in many applications. When needed such coatings can also be formulated and are commercially available to enhance the resistance of any of the products to color fading from protracted exposure to UV light in outdoor or other high sunlight exposure applications. Such coatings also provide suitable dielectric performance so that printed and coated sheets can be held in the mold cavities using electrostatic means without the degradation or dissipation of the electrostatic charge prior to mold closure and completion of the molding process. Satisfactory, but not optimum, UV curable coatings are available from a number of sources by specifying a clear coat that will adhere to lithographic printed images and which exhibits whatever performance factors such as those cited above are needed for the specific application. A suitable series of such coatings has been optimized to enhance the most important properties for the majority of product applications is the GRA series of coatings, which are clear variants of the screen inks previously cited. These coatings are available from Pinnacle Products Group, Ltd. of Dayton Ohio. Such coatings are UV crosslinkable coatings containing an acrylate ester.
The invention makes possible many new capabilities and opens many new opportunities in the field of in-mold decorating. First, the invention allows improving the quality of images that can be in-molded by implementing offset lithography, flexographic and gravure printing as options. Second, the invention provides in-molding approaches that are easier to implement and have lower production costs by enhancing the effectiveness of electrostatic adhesion and often allowing in-molding without modifying molds. Third, the invention provides products and images which are more robust and durable, particularly in the areas of UV induced fading, abrasion, and slip resistance in underfoot applications. Fourth, the invention provides methods that lower the scrap rates from unsuccessful attempts by improving the stability of the in-mold graphic element during molding and by positive fusion of the graphic element into the surface of the molded part. Fifth, the invention provides for implementation with minimum impact on production process cycle times, including the implementation of robotic handling, hence making in-mold decorating more cost competitive. Sixth, the invention provides the ability to implement in-mold decoration in thermosetting and vulcanization applications opening a plurality of new products to such decoration. Seventh, the invention provides for implementing in-mold and in-line decorating in a wider range of molding techniques including extrusion and thermoforming while simplifying injection molding and blow molding. Eighth, the invention provides a plurality of new options for decorated molded products through such applications as the manufacture of polyolefin products that can be screen printed without using specialized inks or corona treatments, the ability to attach metallized foils to molded parts, and the ability to attach pressure sensitive adhesive materials such as reflective tape to materials to which they would not otherwise adhere. Ninth, the invention provides new or improved opportunities for permanent product labeling in thermoplastic, thermosetting, and vulcanizable product applications allowing in-molding of safety labels, product identification labels, product serialization labels, product ownership labels for security purposes, part number labels, life cycle tracking labels, and production lot identification labels containing text, logos, graphics or barcodes. Tenth, the invention provides for identifying that said products have been altered or misused, thus providing an added security feature to the finished molded product. Eleventh, the invention allows for the in-mold decoration of deep dimensional and three dimensional molded parts. Twelfth, the invention eliminates concerns over the differences in polymer shrink rates between an in-moldable label and the polymer to which it is molded. Lastly, the invention allows manufacturers of an in-mold decorated product to have the image assume the texture of the underlying molded material as imparted by the mold surface due to the inherent flexibility of the sheet materials used.
Accordingly, it is an object of the present invention to provide methods for in-mold decorating which provides high quality images onto extruded and molded parts, and to provide products produced by those methods. These, and other features and advantages, will become apparent from the following detailed description and the appended claims.
The present invention is illustrated by the following representative, but non-limiting, examples.